As early as 1776, Alessandro Volta recorded his observation that a combustible gas is generated from decaying vegetable matter in the sediments of lakes and ponds. By 1906 this process was known to be a complex microbial fermentation that generated methane by the bioconversion of cellulose and carbon dioxide. For years the development of methane generators, making use of sewage sludge, took place, usually on a large scale by municipalities. There are, for instance, many sewerage disposal plants which make use of sewage sludge for generating a gas which is subsequently burned to provide energy for use in carrying on the sewage processes. Many of these methane generators that use sewage sludge are able to sell the excess gas for a profit. This led to the development of methane generators for converting animal manure to produce methane, commonly referred to as "biogas".
It has been contemplated that there are certain desirable aspects in making use of the methane generating process in rural homes and, particularly on farms. Small domestic methane generators have been installed since 1946 in India where the Gandhian philosophy of coexisting with nature has been particularly strong. This philosophy stresses simplicity, self-sufficiency, and harmony with nature. Most of these small domestic generators have made use of animal manure and, therefore, have been restricted to farms. However, there is no reason why the concept cannot be applied to domestic installation in any location, particularly if unmilled agricultural and domestic waste are used as the basic feed stock. Nevertheless, one of the major problems encountered in attempting to popularize such small domestic methane generators has been the fact that the coarse solids in the sludge have a tendency to rise to the top, cake up and fail to decompose. Such a mat of solids tends to accumulate on the upper region of the body of liquid slurry, so that gas production is drastically reduced. In order to eliminate such stratification, expensive particle reduction by milling the solids and keeping the particles in suspension by costly process of continuous agitation and mixing are necessary. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a methane generator in which gas is generated from unpulverized organic material and is allowed to flow freely from a body of liquid sludge into a hollow collector.
Another object of this invention is the provision of a methane generator in which organic waste solids are maintained submerged in the body of waste slurry.
A further object of the present invention is the provision of a methane generator, particularly adapted for domestic or farm use operating with a slurry of domestic waste, animal manure and many other types of unpulverized organic matter.
It is another object of the instant invention to provide a methane generator which is simple in construction, which is inexpensive to manufacture, and which is capable of a long life of useful service with a minimum of maintenance.
A still further object of the invention is the provision of a methane generator for domestic or farm use whose cost can be amortized over a fairly short period of time and which is operated with a minimum of care i.e., has a passive operation.
It is a further object of the invention to provide a methane generator which is capable of directly converting coarse organic material such as paper, leaf makings, grass clippings, lumps of garbage, chopped hay or pieces of crop residue without first milling the organic material and making it into slurry.